Various optical fibers such as a bundle fiber, in which a plurality of optical fibers are bundled together, and a large diameter fiber having a diameter larger than a standard optical fiber are used for data signal communications. In addition, for example, such optical fiber is used as a light guide in an exposure device for a semiconductor wafer. The light guide guides exposure light to a light exit section to expose the semiconductor wafer to the exposure light (see U.S. Pat. No. 7,059,778, corresponding to Japanese Patent Laid-Open Publication No. 2003-322730). In a light source apparatus of an endoscope, an optical fiber is used as a light guide which guides illumination light to a distal end of the endoscope so as to illuminate a body cavity of a patient (see Japanese Patent Laid-Open Publication No. 2000-199864).
In the case where the optical fiber is used as the light guide for guiding the exposure light as described in U.S. Pat. No. 7,059,778, a desired resist pattern cannot be produced if the radiation of light on the wafer is not uniform. In the case where the optical fiber is provided in the endoscope as the light guide for illumination as described in Japanese Patent Laid-Open Publication No. 2000-199864, it becomes difficult to find a lesion if the light guided by the light guide has nonuniform light amount distribution and such light reflects off an object of interest having high reflectivity or uneven surfaces, because an image taken with the endoscope also becomes uneven in brightness.
Conventionally, to increase uniformity of the light amount distribution of light from a light guide, the number of optical fibers for forming a bundle fiber is increased. Alternatively or in addition, in U.S. Pat. No. 7,059,778, a position of exit light and its light amount distribution are detected at a light exit surface of the optical fiber, and the light amount distribution of the light incident on the optical fiber is controlled in accordance with the detection results. In Japanese Patent Laid-Open Publication No. 2000-199864, the uniformity of a light amount distribution of exit light from an optical fiber is increased across its diameter direction by shifting a direction of a light incident end of the optical fiber to a direction orthogonal to an optical axis.
However, in U.S. Pat. No. 7,059,778, a device for detecting the position or the light amount distribution of the exit light, or a device for controlling the light amount distribution is required. In Japanese Patent Laid-Open Publication No. 2000-199864, a mechanism to shift the light incident end of the optical fiber is required. In either case, the light guide is upsized and additional cost is required for increasing the uniformity of the light amount distribution.
Generally, in a case where light is incident on a multimode optical fiber through which light of various modes is propagated, or where multimode optical fibers are optically connected, light (laser) is input or the multimode optical fibers are optically connected at an angle not more than a numerical aperture (NA) of the optical fiber, namely, an acceptance angle of the optical fiber, in view of stabilizing the incident light or the connection of the multimode optical fibers. Accordingly, the exit light from the center portion of the multimode optical fiber has higher light amount than the exit light from a peripheral portion thereof. Thus, the light amount distribution at the light exit surface of the multimode optical fiber is not uniform.